Colorization of B&W videos on AE CS5

I have an idea to colorize black and white videos in After Effects, and please comment if you have anything to improve it, because I really want to color my old movies.

I plan to open my video
Than make a new null object
Then use Motion Tracking on the null object layer
Then use masking and color correction to add the color
Attach the color layer to the motion tracked null object

Can this work? I am new to AE, so please pardon. Also, I have a part of my black and white film where a man move his head and hands a lot, how can I keep the color layer in sync with the movement of his hands and body, and not have the color overlap into the background?
Thank you for any help you can give.